The objectives of this research are to provide insight into: 1) the relation of membrane sterol composition to biochemical expressions of glial differentiation and to ionic flux, 2) the relation of cytoskeletal structures to HMG-CoA reductase and cholesterol biosynthesis, 3) the relation of fatty acyl alterations to cholesterol biosynthesis, membrane lipid composition and oligodendroglial differentiation, and 4) the interrelations of lipid synthesis and specific events in brain development. The relation of membrane sterol composition to biochemical expressions of glial differentiation and to ionic flux will be studied in cultured C-6 glial cells, which can be induced to exhibit oligodendroglial or astrocytic properties. Membrane sterol composition will be altered by specific inhibitors of cholesterol biosynthesis, e.g., compactin and U18666A, which operate at different sites in the biosynthetic pathway. Correction of the lipid defects by addition of exogenous sources of sterol will help determine the precise relationships between membrane lipid alterations and the observed effects. The relation of cytoskeletal structures to HMG-CoA reductase and cholesterol biosynthesis will be studied principally in cultured C-6 glia. We will determine: 1) the relationships between tubulin polymerization and the activity of HMG-CoA reductase, 2) the cellular specificity of the relationships, 3) the mechanism of the changes in reductase activity, and 4) the consequences of alterations in reductase activity re: synthesis of nonsterol isoprenoid compounds, as well as sterol, and re: membrane lipid composition. The relations of fatty acyl alterations to cholesterol biosynthesis, membrane lipid composition and oligodendroglial differentiation will be studied in cultured C-6 glia. Fatty acyl alterations will be produced by providing the fatty acids to cells in serum-free medium. The interrelations of lipid synthesis, cellular proliferation, neuronal and glial differentiation, and myelination will be studied in aggregating brain cell cultures. We will determine the major correlates of these specific developmental events re: sterol and fatty acid (de novo and chain elongation systems) synthesis and re: the regulation of these pathways at the enzyme level. The specific roles of sterols in these events will be determined by utilization of specific inhibitors.